An IGBT (Insulated Gate Bipolar Transistor), a diode or the like is used as a semiconductor device used for a power conversion device such as an inverter. The diode is generally connected in reverse parallel to the IGBT and is used as a free wheeling diode. Thus, the diode is sometimes called a FWD (Free Wheeling Diode).
For characteristic improvement of the power conversion device such as an inverter, characteristic improvement of the FWD is important in addition to characteristic improvement of the IGBT. Characteristics to be improved include an ON voltage (voltage drop in a conduction state), a recovery time (extinction time of recovery current at reverse recovery), a safe operation region during recovery (operation region in which damage does not occur even if voltage is applied in a state where reverse recovery current flows), and current and voltage vibration during recovery. Especially, to shorten the recovery time is important. Incidentally, in the following, the reverse recovery is called recovery.